Bottom Line:
Moreover, lentiviral vector-based gene introduction did not result in any significant changes in cytomorphology and cell viability.Although the expression of IL8, STAT1, and IDO1 genes was up-regulated in transduced hMDM, such alternation in gene expression did not affect the neuroprotective effect of Hutat2:Fc.Our study demonstrated that lentivirus-mediated gene transfer could efficiently deliver the Hutat2:Fc gene into primary hMDM and does not lead to any significant changes in hMDM immune-activation.

Background: HIV-1 Tat is essential for HIV replication and is also a well-known neurotoxic factor causing HIV-associated neurocognitive disorder (HAND). Currently, combined antiretroviral therapy targeting HIV reverse transcriptase or protease cannot prevent the production of early viral proteins, especially Tat, once HIV infection has been established. HIV-infected macrophages and glial cells in the brain still release Tat into the extracellular space where it can exert direct and indirect neurotoxicity. Therefore, stable production of anti-Tat antibodies in the brain would neutralize HIV-1 Tat and thus provide an effective approach to protect neurons.

Methods: We constructed a humanized anti-Tat Hutat2:Fc fusion protein with the goal of antagonizing HIV-1 Tat and delivered the gene into cell lines and primary human monocyte-derived macrophages (hMDM) by an HIV-based lentiviral vector. The function of the anti-Tat Hutat2:Fc fusion protein and the potential side effects of lentiviral vector-mediated gene transfer were evaluated in vitro.

Results: Our study demonstrated that HIV-1-based lentiviral vector-mediated gene transduction resulted in a high-level, stable expression of anti-HIV-1 Tat Hutat2:Fc in human neuronal and monocytic cell lines, as well as in primary hMDM. Hutat2:Fc was detectable in both cells and supernatants and continued to accumulate to high levels within the supernatant. Hutat2:Fc protected mouse cortical neurons against HIV-1 Tat86-induced neurotoxicity. In addition, both secreted Hutat2:Fc and transduced hMDM led to reducing HIV-1BaL viral replication in human macrophages. Moreover, lentiviral vector-based gene introduction did not result in any significant changes in cytomorphology and cell viability. Although the expression of IL8, STAT1, and IDO1 genes was up-regulated in transduced hMDM, such alternation in gene expression did not affect the neuroprotective effect of Hutat2:Fc.

Conclusions: Our study demonstrated that lentivirus-mediated gene transfer could efficiently deliver the Hutat2:Fc gene into primary hMDM and does not lead to any significant changes in hMDM immune-activation. The neuroprotective and HIV-1 suppressive effects produced by Hutat2:Fc were comparable to that of a full-length anti-Tat antibody. This study provides the foundation and insights for future research on the potential use of Hutat2:Fc as a novel gene therapy approach for HAND through utilizing monocytes/macrophages, which naturally cross the blood-brain barrier, for gene delivery.

Fig3: Evaluation of the biological binding function of Hutat2:Fc and protective effects of Hutat2:Fc against HIV-1 Tat86-mediated toxicity in HTB-11 cells.(A) Specific binding of Hutat2:Fc to HIV-1 Tat. HIV-1 Tat86 (Clade B) loaded nitrocellular membranes (NCM) were incubated with cell culture supernatants collected from HR-Hutat2-transduced HTB-11 (HTB-Hutat2), U937 (U937-Hutat2), or hMDM (hMDM-Hutat2) at 4°C overnight followed by incubation with rabbit anti-human IgG(H+L) and goat anti-rabbit IgG HRP conjugated antibodies. Specific binding was visualized by the color deposition on the NCM. The Tat86-loaded membrane incubated with rabbit anti-Tat serum served as a positive control (Pos Ctl) while incubated with cell culture supernatant from HR-A3H5 transduced HTB-11 served as a negative control (HTB-A3H5). The NCM loaded with Tat dilution buffer was used as a blank control (BLK Ctl). (B) Functional antagonization of Hutat2:Fc against HIV-1 Tat86-induced toxicity in HTB-11 cells by an MTT assay. The OD570 value of untreated HTB-11 cells was arbitrarily defined as 100% cell viability. The relative cell viability (%) was expressed as a percentage relative to the untreated control cells. The cell viability was significantly higher for the cells treated with the conditioned mediums from transduced cells releasing Hutat:Fc when compared to the cultures that received Tat86 (500 nM) alone (*P <0.01 for HTB-Hutat2 medium; #P <0.05 for U937-Hutat2 medium, and hMDM-Hutat2 medium). (C) Protection of HR-Hutat2 transduction against Tat86-induced toxicity by an MTT assay. No significant difference of cell viability was detected between normal and vector HR-Hutat2 transduced HTB-11 cells (HTB-Hutat2) (P >0.05). However, the cell viability of HTB-11 transduced with the vector HR-Hutat2 was significantly higher than that of HTB-A3H5 in the presence of HIV-1 Tat86 (500 nM) (*P <0.01). All experiments were performed in quadruplicate. Error bars denote the s.e.m.

Mentions:
After confirming the stable expression of Hutat2:Fc, an immunoblot assay was employed to assess the specific binding ability of secreted Hutat2:Fc to HIV-1 Tat. Recombinant HIV-1 Tat86 (Clade B) was diluted and blotted onto a NCM with the dilution buffer included as a blank control. The conditioned medium from HR-A3H5 transduced HTB-11 served as a negative control and anti-HIV-1 Tat serum served as a positive control. The conditioned mediums containing anti-HIV-1 Tat Hutat2:Fc from transduced HTB-11 and U937 cells as well as hMDM bound specifically to HIV-1 Tat86 while no binding was detected to neither the blank control nor the secreted A3H5:Fc control (Figure 3A). In addition, to confirm that the Hutat2:Fc was able to bind the unaggregated form of Tat, Tat86 was separated by SDS-PAGE electrophoresis and Western blot assay was performed using the conditioned medium from transduced cells as primary antibodies. In accordance with the DIBA results, Hutat2:Fc from HR-Hutat2 transduced cells could specifically bind to Tat86 (14 kDa), whereas A3H5:Fc from HR-A3H5 transduced HTB-11 could not (Additional file 3). These tests demonstrate that the secreted Hutat2:Fc is able to bind specifically and sufficiently to HIV Tat86 as a fully-functional HIV-1 Tat antibody in vitro, as designed.Figure 3

Fig3: Evaluation of the biological binding function of Hutat2:Fc and protective effects of Hutat2:Fc against HIV-1 Tat86-mediated toxicity in HTB-11 cells.(A) Specific binding of Hutat2:Fc to HIV-1 Tat. HIV-1 Tat86 (Clade B) loaded nitrocellular membranes (NCM) were incubated with cell culture supernatants collected from HR-Hutat2-transduced HTB-11 (HTB-Hutat2), U937 (U937-Hutat2), or hMDM (hMDM-Hutat2) at 4°C overnight followed by incubation with rabbit anti-human IgG(H+L) and goat anti-rabbit IgG HRP conjugated antibodies. Specific binding was visualized by the color deposition on the NCM. The Tat86-loaded membrane incubated with rabbit anti-Tat serum served as a positive control (Pos Ctl) while incubated with cell culture supernatant from HR-A3H5 transduced HTB-11 served as a negative control (HTB-A3H5). The NCM loaded with Tat dilution buffer was used as a blank control (BLK Ctl). (B) Functional antagonization of Hutat2:Fc against HIV-1 Tat86-induced toxicity in HTB-11 cells by an MTT assay. The OD570 value of untreated HTB-11 cells was arbitrarily defined as 100% cell viability. The relative cell viability (%) was expressed as a percentage relative to the untreated control cells. The cell viability was significantly higher for the cells treated with the conditioned mediums from transduced cells releasing Hutat:Fc when compared to the cultures that received Tat86 (500 nM) alone (*P <0.01 for HTB-Hutat2 medium; #P <0.05 for U937-Hutat2 medium, and hMDM-Hutat2 medium). (C) Protection of HR-Hutat2 transduction against Tat86-induced toxicity by an MTT assay. No significant difference of cell viability was detected between normal and vector HR-Hutat2 transduced HTB-11 cells (HTB-Hutat2) (P >0.05). However, the cell viability of HTB-11 transduced with the vector HR-Hutat2 was significantly higher than that of HTB-A3H5 in the presence of HIV-1 Tat86 (500 nM) (*P <0.01). All experiments were performed in quadruplicate. Error bars denote the s.e.m.

Mentions:
After confirming the stable expression of Hutat2:Fc, an immunoblot assay was employed to assess the specific binding ability of secreted Hutat2:Fc to HIV-1 Tat. Recombinant HIV-1 Tat86 (Clade B) was diluted and blotted onto a NCM with the dilution buffer included as a blank control. The conditioned medium from HR-A3H5 transduced HTB-11 served as a negative control and anti-HIV-1 Tat serum served as a positive control. The conditioned mediums containing anti-HIV-1 Tat Hutat2:Fc from transduced HTB-11 and U937 cells as well as hMDM bound specifically to HIV-1 Tat86 while no binding was detected to neither the blank control nor the secreted A3H5:Fc control (Figure 3A). In addition, to confirm that the Hutat2:Fc was able to bind the unaggregated form of Tat, Tat86 was separated by SDS-PAGE electrophoresis and Western blot assay was performed using the conditioned medium from transduced cells as primary antibodies. In accordance with the DIBA results, Hutat2:Fc from HR-Hutat2 transduced cells could specifically bind to Tat86 (14 kDa), whereas A3H5:Fc from HR-A3H5 transduced HTB-11 could not (Additional file 3). These tests demonstrate that the secreted Hutat2:Fc is able to bind specifically and sufficiently to HIV Tat86 as a fully-functional HIV-1 Tat antibody in vitro, as designed.Figure 3

Bottom Line:
Moreover, lentiviral vector-based gene introduction did not result in any significant changes in cytomorphology and cell viability.Although the expression of IL8, STAT1, and IDO1 genes was up-regulated in transduced hMDM, such alternation in gene expression did not affect the neuroprotective effect of Hutat2:Fc.Our study demonstrated that lentivirus-mediated gene transfer could efficiently deliver the Hutat2:Fc gene into primary hMDM and does not lead to any significant changes in hMDM immune-activation.

Background: HIV-1 Tat is essential for HIV replication and is also a well-known neurotoxic factor causing HIV-associated neurocognitive disorder (HAND). Currently, combined antiretroviral therapy targeting HIV reverse transcriptase or protease cannot prevent the production of early viral proteins, especially Tat, once HIV infection has been established. HIV-infected macrophages and glial cells in the brain still release Tat into the extracellular space where it can exert direct and indirect neurotoxicity. Therefore, stable production of anti-Tat antibodies in the brain would neutralize HIV-1 Tat and thus provide an effective approach to protect neurons.

Methods: We constructed a humanized anti-Tat Hutat2:Fc fusion protein with the goal of antagonizing HIV-1 Tat and delivered the gene into cell lines and primary human monocyte-derived macrophages (hMDM) by an HIV-based lentiviral vector. The function of the anti-Tat Hutat2:Fc fusion protein and the potential side effects of lentiviral vector-mediated gene transfer were evaluated in vitro.

Results: Our study demonstrated that HIV-1-based lentiviral vector-mediated gene transduction resulted in a high-level, stable expression of anti-HIV-1 Tat Hutat2:Fc in human neuronal and monocytic cell lines, as well as in primary hMDM. Hutat2:Fc was detectable in both cells and supernatants and continued to accumulate to high levels within the supernatant. Hutat2:Fc protected mouse cortical neurons against HIV-1 Tat86-induced neurotoxicity. In addition, both secreted Hutat2:Fc and transduced hMDM led to reducing HIV-1BaL viral replication in human macrophages. Moreover, lentiviral vector-based gene introduction did not result in any significant changes in cytomorphology and cell viability. Although the expression of IL8, STAT1, and IDO1 genes was up-regulated in transduced hMDM, such alternation in gene expression did not affect the neuroprotective effect of Hutat2:Fc.

Conclusions: Our study demonstrated that lentivirus-mediated gene transfer could efficiently deliver the Hutat2:Fc gene into primary hMDM and does not lead to any significant changes in hMDM immune-activation. The neuroprotective and HIV-1 suppressive effects produced by Hutat2:Fc were comparable to that of a full-length anti-Tat antibody. This study provides the foundation and insights for future research on the potential use of Hutat2:Fc as a novel gene therapy approach for HAND through utilizing monocytes/macrophages, which naturally cross the blood-brain barrier, for gene delivery.